1. Field of the Invention
The present invention relates to a loop locating apparatus and loop locating method for identifying a location of occurrence of a fault occurring in an IP (Internet Protocol) network, for example, an IP Multicast Layer 3 Network including a plurality of routers, in particular a Layer 3 loop fault.
2. Description of the Related Art
As will be explained later with reference to the figures (FIG. 16), in an IP Multicast Layer 3 Network, sometimes a Layer 3 loop fault (hereinafter referred to simply as a “loop”) occurs. This “loop” means the situation, when transmitting information packets by multicasting from one terminal to a plurality of terminals in a Layer 3 Network, where information packets end up traveling back and forth in a loop between two adjoining routers of the plurality of routers and are no longer forwarded to the terminals further on.
A leading cause of such a “loop” is an error in setting of the equipment in the routing tables in the two routers and the consequent failure of setting routing information for the information packets. In such a case, the two routers use the default routing information instead of the not set routing information. At this time, if the router A among the two routers A and B has default routing information to the path to the router B and the router B has default routing information to the path to the router A, the information packets attempting to pass through the routers A and B end up traveling back and forth between the routers A and B again and again leading to the occurrence of a loop.
If this happens, the information packets will end up disappearing after forming 256 loops since the TTL (Time to Live) setting is for example 256. Also, the multicast traffic will therefore become enormous. In the end, the network as a whole will be overloaded. Therefore, when detecting the occurrence of such a loop, it is necessary to quickly identify the location of occurrence of that loop and speedily eliminate the cause of the loop.
As known art relating to the present invention, there are Japanese Patent Publication (A) No. 8-288982 and Japanese Patent Publication (A) No. 1-223854. Japanese Patent Publication (A) No. 8-288982 discloses a “relay communication system” which detects information on the remaining permissible number of relay operations, a value which corresponds to the TTL, and suspends relay operations of the data when the number reaches “0”. Further, Japanese Patent Publication (A) No. 1-223854 discloses a “test method for a data transmission system” which transmits a test frame to a network transmission system, analyzes a test response frame received back, checks if a response as expected is returned, and if the response is as expected, judges that operation is normal.
Therefore, neither of the above patent publications suggests at all the later explained characterizing feature of the present invention, that is, “sending a series of inspection packets with successively incremented TTLs to a network and analyzing the packets returned from the network to the source of the packets so as to identify the location of occurrence of the loop”.
As a general technique for identifying the location of occurrence of a loop, there is the “traceroute”. As explained later with reference to the figures (FIG. 17), however, when a multicast stream loops, the situation is sometimes different from a unicast route and therefore the “traceroute” technique sometimes cannot determine the correct route.
Therefore, in the past, the practice has been to log in to each router by a Telnet etc. and individually collect the setting information relating to the multicast. Accordingly, since the method of setting each piece of equipment differs, there was the first problem that it was necessary to know how to confirm the setting information for all of the equipment.
Further, it was necessary to collect the setting information for the equipment from all of the routers for each individual multicast address and to manually confirm the multicast route. For this reason, there was the second problem that tremendous time was required for identifying the location of occurrence of a loop fault.